In communication networks based on the Long Term Evolution, LTE, specifications promulgated by the Third Generation Partnership Project, or 3GPP, two radio frame structures are supported; namely, a “type 1” structure that is applicable to Frequency Division Duplexing, FDD, and a “type 2” structure applicable to Time Division Duplexing, TDD. In both frame structure types, each radio frame of 10 ms is divided into two half-frames of 5 ms, and each half-frame includes five subframes of length 1 ms.
Further, in frame structure type 2, each subframe is a downlink subframe, an uplink subframe, or a special subframe, giving rise to different TDD configurations. Such configurations are in the table of FIG. 1. These configurations are defined in Table 4.2-2 of the 3GPP Technical Specification, TS 36.211.
The supported uplink-downlink configurations in LTE TDD are depicted in FIG. 1, where, for each subframe in a radio frame, “D” denotes the subframe is reserved for downlink transmissions, “U” denotes the subframe is reserved for uplink transmissions and “S” denotes a special subframe with the three fields: DwPTS, GP and UpPTS. The length of DwPTS and UpPTS is given by the table of FIG. 1 subject to the total length of DwPTS, GP and UpPTS being equal to 1 ms. Each subframe consists of two slots, each of length 0.5 ms.
Uplink-downlink configurations with both 5 ms and 10 ms downlink-to-uplink switch-point periodicity are supported. In case of 5 ms downlink-to-uplink switch-point periodicity, the special subframe exists in both half-frames.
In case of 10 ms downlink-to-uplink switch-point periodicity, the special subframe exists in the first half-frame only. Subframes 0 and 5 and DwPTS are always reserved for downlink transmission regardless of switchpoint periodicity. UpPTS and the subframe immediately following the special subframe are always reserved for uplink transmission.
In a TDD cell within a wireless communication network, a TDD configuration is characterized by both the uplink-downlink configuration and the special subframe configuration. Therefore the term “TDD configuration” used hereinafter refers to a combination of an uplink-downlink configuration configured in a TDD cell, e.g. one of the configurations depicted in the table of FIG. 1, along with a special subframe configuration, e.g., one of the configurations depicted in the table of FIG. 2. The choice of uplink-downlink configuration and the special subframe configuration are not necessarily related to each other. Of course, it will be understood that these are example configurations and additional TDD configurations may be introduced in the future, and the teachings herein are not limited to these example configurations.
Dynamic TDD, e.g., dynamically changing TDD configurations, may be used to better adapt to changing network deployments and usage. For example, it is envisioned that there will be more and more localized traffic in the future, where most of network users will be in hotspots, or in indoor areas, or in residential areas. These users will be located in clustered nature and will produce different UL and DL traffic at different times. This circumstance essentially means that a dynamic feature to adjust the UL and DL resources to instantaneous (or near instantaneous) traffic variations would be required in future local area cells. TDD has a potential feature where the usable band can be configured in different time slots to either UL or DL. It allows for asymmetric UL/DL allocation, which is a TDD-specific property, and not possible in FDD. There are seven different UL/DL allocations in LTE, providing 40%-90% DL resources as shown in the table of FIG. 1. The different TDD configurations are also shown in FIG. 3.
In current networks, UL/DL configuration is semi-statically configured, thus it may not match the instantaneous traffic situation. This mismatch results in inefficient resource utilization in both UL and DL, especially in cells with a small number of users. Dynamic TDD addresses this issue by dynamically configuring the TDD UL/DL asymmetry to better match the current traffic situation, and thereby optimize or at least improve the user experience. See 3GPP TR 36.828 V2.0.0 (2012-06). The dynamic TDD approach also can be utilized to reduce network energy consumption.
Thus, the typical use of fixed TDD configurations in existing TDD networks, which fixes which subframes are uplink subframes and which subframes are downlink subframes, should be understood as limiting the ability to address changing uplink/downlink asymmetry arising from varying traffic situations. One approach to increasing TDD configuration flexibility, at least in some scenarios, is based on the idea that each subframe (or part of a subframe) belongs to one of three different types:                Downlink subframes (exist in Rel-8) are used (among other things) for transmission of downlink data, system information, control signaling and hybrid-ARQ feedback in response to uplink transmission activity. The UE monitors PDCCH as in Rel-8, i.e., it may receive scheduling assignments and scheduling grants. Special subframes are similar to downlink subframes except, in addition to the downlink part, they also include a guard period as well as a small uplink part in the end of the subframe to be used for random access or sounding.        Uplink subframes (exist in Rel-8) are used (among other things) for transmission of uplink data, uplink control signaling (channel-status reports), and hybrid-ARQ feedback in response to downlink data transmission activity. Data transmission on the PUSCH in uplink subframes is controlled by uplink scheduling grants received on a PDCCH in an earlier subframe.        Flexible subframes (do not exist in Rel-8), which may be referred to as “DKWTA subframes,” may either be used for uplink or downlink transmissions, as determined by scheduling assignments/grants.        
Semi-static configuration is used to assign each subframe either as uplink or as downlink subframe as illustrated in FIG. 3. The semi-static configuration of subframe types may be accomplished by Medium Access Control, MAC, Control Element or CE, or Radio Resource Control (RRC), or specific Radio Network Temporary Identifier, or RNTI, on the Physical Downlink Control Channel or PDCCH. Configuration information could be part of the system information as in Rel-8. In dynamic TDD, an additional subframe type is added, labelled as “DKWTA” subframes as shown in FIG. 4. The dynamic TDD configuration information can be signaled to terminals in different ways, for example, either by explicitly indicating “UL”, “DL”, or “DKWTA” or by signaling “DL” and “UL” using the Rel-8 signaling message and then using an additional signaling message, understandable by new terminals only, where some UL subframes are changed into Flexible subframes.
From a dynamic TDD enabled UE perspective, Flexible subframes are treated in a similar way as DL subframes unless the UE has been instructed to transmit in a particular Flexible subframe. Expressed differently, Flexible subframes not assigned for uplink transmission from a particular UE are, from a PDCCH perspective, treated as a DL subframe. Hence, the UE monitors several candidate PDCCHs in a Flexible subframe. If the control signaling indicates that the UE is supposed to receive downlink data transmission on the Physical Downlink Shared Channel (PDSCH), the UE will receive and process the PDSCH as in a DL subframe. Similarly, if the control signaling contains an uplink scheduling grant valid for a later subframe, the UE will transmit in the uplink accordingly.
The terms dynamic TDD, flexible TDD, flexible UL/DL allocation, adaptive TDD, reconfigurable TDD, etc., are interchangeably used, but they all refer to the same concept. With dynamic TDD, one or more “dynamic” or “flexible” subframes can be used in different directions of transmission (i.e., UL versus DL) in different cells, which may belong to the same carrier or different carriers. Furthermore, the direction of flexible subframes in a particular cell can be changed over time, e.g., as fast as every radio frame. The controlling radio network node can decide whether and when to change the direction of a flexible subframe independently, or depending upon the TDD configuration used in one or more neighboring TDD cells. In principle any subframe that is not adjacent to “special subframe (S)” can be configured as a flexible subframe. For example in TDD configuration 0, as shown in FIG. 1, any of the subframes 3, 4, 8 and 9 can be configured as a flexible subframe.
While dynamic UL/DL allocation in theory should provide a good match of allocated resources to instantaneous traffic, different UL and DL transmission in neighboring cells also causes issues related to handover, HO, measurements by the UEs.
In LTE, each eNB sends cell configuration information of each cell in the eNB to neighboring eNBs over the X2 interface, as defined in TS 36.423 Release 8. The information also contains TDD-related information, e.g. UL DL configuration, special subframe configuration, etc. In principle, then, Release 8 provides for use of dynamically updated TDD configurations. In practice, however, dynamic TDD configurations have not been used, primarily because of the lack of interference mitigation techniques needed to alleviate interference caused by the use of dynamic TDD configurations. See, e.g., 3GPP TR 36.828 V2.0.0 (2012-06). However, work is ongoing with respect to related procedures. See, e.g., RP-121772, “Further Enhancements to LTE TDD for DL-UL Interference Management and Traffic Adaptation”, WID approved at 3GPP RAN#58.
UEs perform one or more measurements on the signals from the cells neighboring their serving cell. Such measurements support a variety of functions, such as mobility-related functions for cell selection/re-selection, handover, RRC re-establishment, connection release with redirection, minimization-of-drive tests, Self-Organizing Network, SON, positioning, etc. A UE must identify a cell and determine its Physical Cell Identity, PCI, prior to making such measurements. In this regard, PCI determination itself may be viewed as a type of measurement.
To perform requested measurements, the UE may receive measurement configuration information, or assistance data, such as a message or Information Element, IE, sent by an involved network node. The node may be a serving eNB, for example, or a positioning node, or some other node in the network. The information provided to the UE may contain information related to the carrier frequency, Radio Access Technologies or RATs, type of measurement, higher layer time domain filtering, measurement bandwidth related parameters, etc. One type of measurement is Reference Symbol Received Power, or RSRP.
Such measurements are done by the UE on the serving as well as on neighbor cells over known reference symbols or pilot sequences. The measurements may be performed on cells on an intra-frequency carrier, inter-frequency carrier(s), as well as on inter-RAT carriers(s) (depending upon the UE capability to supports other RATs).
The network configures measurement gaps, to enable the UE to make inter-frequency and inter-RAT measurements. Two periodic measurement gap patterns both with a measurement gap length of 6 ms are defined for LTE:                Measurement gap pattern #0 with repetition period 40 ms        Measurement gap pattern #1 with repetition period 80 ms        
In High Speed Packet Access or HSPA, the inter-frequency and inter-RAT measurements are performed in compressed mode gaps, which are also a type of network configured measurement gaps. Some measurements may also require the UE to measure the signals transmitted by the UE in the uplink. The measurements are done by the UE in RRC connected state or in CELL_DCH state (in HSPA), as well as in low activity RRC states (e.g. idle state, CELL_FACH state in HSPA, URA_PCH and CELL_PCH states in HSPA, etc.). In multi-carrier or Carrier Aggregation, CA, scenarios, the UE may perform the measurements on the cells on the primary component carrier, PCC, as well as on the cells on one or more secondary component carriers, or SCCs.
Such measurements are typically performed over longer time duration, e.g., in the order of few 100 ms to few seconds. The same measurements are applicable in single carrier and CA. However, CA contexts may involve different measurement requirements. For the measurement period in a CA scenario may be either more relaxed or more stringent, depending upon whether the SCC is activated or not. The requirement may also depend upon the UE capability, such as whether the UE is able to perform measurements on the SCC without gaps.
In addition to the RSRP measurement identified earlier, the Reference Symbol Received Quality or RSRQ stands as another example of mobility measurements made in LTE. Example mobility measurements in HSPA include Common pilot channel received signal code power, or CPICH RSCP, and CPICH Ec/No (which is a noise-based ratio). Further mobility measurement examples in the context of GSM/GERAN include GSM carrier Received Signal Strength Information or RSSI, and in the context of CDMA2000 include pilot strength for CDMA2000 1×RTT and pilot strength for High Rate Packet Data or HRPD.
As noted, mobility measurements generally include detecting/identifying a cell, which may belong to LTE, HSPA, CDMA2000, GSM, etc. Cell detection includes identifying at least the PCI and subsequently performing the signal measurement (e.g. RSRP) of the identified cell. The UE may also have to acquire the cell global ID, or CGI. In HSPA and LTE, the serving cell can request that the UE acquire the System Information, SI, of the target cell. More specifically, the UE acquires the CGI of the target cell from the SI. The UE may also be requested to acquire other information from the target cell, such as Closed Subscriber Group, CSG, information, CSG proximity detection.
Example positioning measurements in LTE include Reference Signal Time Difference or RSTD measurements, and UE Receive (RX)/Transmit (TX) time difference measurements. The latter measurement requires the UE to perform measurement on the downlink reference signal, as well as on its uplink transmitted signals.
Examples of other measurements useful for radio link maintenance, minimization-of-drive-time, SON, etc., include control channel failure rate or quality estimate measurements, e.g., determination of the Paging channel failure rate and/or the Broadcast channel failure rate. Measurement may also provide detection of physical layer problems, such as detecting whether the UE is in or out of synchronization, and radio link monitoring and/or failure detection.
Still further, Channel State Information, or CSI, measurements performed by the UE are used for scheduling, link adaptation, etc., by the network. Examples of CSI measurements include the determination Channel Quality Information, CQI, which may comprise a value indicating a signal-to-noise-ratio, SNR, or signal-to-noise-plus-interference ratio, SINR, at the UE, a Precoder Matrix Indicator, PMI, which may index into a known codebook of multi-antenna transmit precoders or otherwise identify a Precoder Matrix suggested for use in transmitting to the UE, and a Rank Indicator, RI, which indicates the transmission rank or number of spatial multiplexing layers that can be supported by the UE given measured channel conditions.
At least some of the radio measurements performed by the UE are used by the UE for one or more radio operational tasks. Examples of such tasks are reporting the measurements to the network, which in turn may use them for various tasks. For example in the RRC connected state, the UE reports radio measurements to the serving node. In response to the reported UE measurements, the serving network node takes certain decisions, e.g., it may send mobility commands to the UE for the purpose of initiating cell changes. Examples of cell change are handover, RRC connection re-establishment, RRC connection release with redirection, Primary or PCell change in CA, etc. Cell reselection represents an example of cell change when the UE is in an idle or low activity state. As another example the UE may itself use the radio measurements for performing tasks, such as cell selection, cell reselection etc.
Of course, radio network nodes, such as Node Bs in WCDMA networks and eNBs in LTE networks, make certain radio measurements to support mobility, positioning, link adaptation, scheduling, loading balancing, admission control, interference management and/or mitigation, etc. These measurements may be performed on signals transmitted by the radio network node and/or on signals received by the radio network node, and example measurements include SNR or SINR determinations, Received Interference Power or RIP measurements, Block Error Rate, BLER, estimations, propagation delay measurements, transmit carrier power, transmit power(s) of one or more other signals, e.g., of reference signals, along with measurements for positioning. The teachings herein will be understood as being applicable to these and the previously discussed types of measurements.
As a further consideration, Release 10 for LTE specifies time domain enhanced Inter-Cell Interference Coordination or eICIC, for use in mitigating interference in so-called heterogeneous networks. Such networks comprise a mix of high power and lower power nodes. For example, a heterogeneous network may include a number of eNBs or other high-power base stations, sometimes referred to as “macro” base stations, each providing service in one or more “macro” cells that may be regarded as comprising a “macro” layer of the network. One or more of these macro cells are overlaid by a smaller, “micro” or “pico” cell or hotspot, served by a low-power base station or access point. Such low-power nodes are often referred to as micro, pico, or femto base stations or nodes. A given micro node may comprise a Home eNB, HeNB, or may simply comprise one or more low-power base stations used to extend or enhance coverage within a macro cell.
According to the time domain eICIC scheme, a time domain pattern of low interference subframes, which are also referred to as “low interference patterns” or Almost Blank Subframe, ABS, patterns. The low interference subframes are configured in an aggressor node, which may be a macro eNB. More specifically, an ABS pattern is configured in an aggressor cell to protect resources in subframes in a victim cell that receives strong inter-cell interference. The victim cell may be a pico cell that overlays or is nearby the aggressor cell.
ABS subframes are typically configured with reduced transmit power or no transmit power and/or reduced activity on some of the physical channels. In an ABS subframe, the basic common physical channels, such as Common Reference Signal, CRS, Primary Synchronization Signal, PSS, Secondary Synchronization Signal, SSS, Primary Broadcast Channel, PBCH, and System Information Block 1, or SIB1, are transmitted to ensure the proper operation of legacy UEs.
The ABS pattern can also be categorized as non-MBSFN and MBSFN, wherein “MBSFN” denotes Multi-cast/Broadcast Single Frequency Network. In a non-MBSFN ABS pattern, the ABS can be configured in any subframe, including MBSFN or non-MBSFN configurable subframes. In a MBSFN ABS pattern, an ABS can be configured only in MBSFN configurable subframes, i.e., subframes 1, 2, 3, 6, 7 and 8 in FDD and subframes 3, 4, 7, 8 and 9 in TDD.
The serving eNB (e.g. a pico eNB) signals one or more measurement patterns (also referred to as measurement resource restriction patterns), to inform a UE about the resources or subframes which the UE should use for performing measurements on a target victim cell (e.g. the serving pico cell and/or neighboring pico cells). The patterns can be different for serving cell measurements, neighbor cell measurements, etc. The resources or subframes on which the measurements are to be done by the UE overlap with ABS subframes in the aggressor cell(s). As such, these resources or subframes within a measurement pattern are protected from aggressor cell interference and are interchangeably also referred to as “protected subframes” or “restricted subframes.”
The serving eNB ensures that each measurement pattern contains at least a certain number of protected subframes in every radio frame—e.g., one to two—to facilitate the performance of measurements by a UE. Without the inclusion of protected subframes, the UE generally cannot meet the predefined measurement requirements, when the UE is configured with measurement patterns related to operation in the heterogeneous network.
Turning to multi-carrier or CA, as referenced earlier, such techniques offer the opportunity to enhance peak rates. Using LTE as an example case, multiple 20 MHz carriers or even smaller carriers (e.g. 5 MHz) can be aggregated in the UL and/or on DL. Each carrier in a multi-carrier or CA system is generally termed as a component carrier, CC, or sometimes referred to simply as a “cell.” Regardless, each CC represents an individual carrier in a multi-carrier system. The use of CA also may be referred to as a “multi-carrier system,” “multi-cell operation,” “multi-carrier operation,” or “multi-carrier” transmission and/or reception.
CA may be used for transmission of signaling and data in the uplink and/or downlink directions. One of the CCs in CA operates as the PCC or simply primary carrier or even anchor carrier. The remaining carriers are SCCs, as mentioned earlier herein, or simply secondary carriers or even supplementary carriers. Generally the primary or anchor CC carries the essential UE-specific signaling. The primary CC (aka PCC or PCell) exists in both uplink and downlink directions in CA. In case there is a single UL CC, the PCell is on that CC. The network may assign different primary carriers to different UEs operating in the same sector or cell.
Therefore, a UE has more than one serving cell in the downlink and/or in the uplink: one primary serving cell and one or more secondary serving cells operating on the PCC and SCC respectively. The serving cell is interchangeably called as primary cell, PCell, or primary serving cell, PSC. Similarly the secondary serving cell is interchangeably called as secondary cell, SCell, or secondary serving cell, SSC. Regardless of the terminology, the PCell and SCell(s) enable the UE to receive and/or transmit data. More specifically the PCell and SCell exist in the DL and UL for the reception and transmission of data by the UE. The remaining non-serving cells on the PCC and SCC are called neighbor cells.
The CCs belonging to the CA may belong to the same frequency band (aka intra-band CA) or to different frequency band (inter-band CA) or any combination thereof (e.g. 2 CCs in band A and 1 CC in band B). Inter-band CA includes carriers distributed over two bands in LTE. Furthermore, the CCs in intra-band CA may be adjacent or non-adjacent in frequency domain (aka intra-band non-adjacent CA). A hybrid CA that includes intra-band adjacent, intra-band non-adjacent and inter-band is also possible. Using carrier aggregation between carriers of different technologies is also referred to as “multi-RAT carrier aggregation” or “multi-RAT-multi-carrier system” or simply “inter-RAT carrier aggregation.” For example, the carriers from a WCDMA network and an LTE network may be aggregated. Another example is the aggregation of LTE and CDMA2000 carriers. Yet another example is the aggregation of LTE FDD and LTE TDD carriers. For the sake of clarity the carrier aggregation within the same technology as described can be regarded as “intra-RAT” or simply “single RAT” carrier aggregation.
Multi-carrier operation may also be used in conjunction with multi-antenna transmission. For example signals on each CC may be transmitted by a eNB to a UE over two or more antennas. Generally, the CCs in a CA deployment may or may not be co-located in the same site or base station or radio network node (e.g. relay, mobile relay etc). For instance the CCs may originate (be transmitted or received) at different locations (e.g. from non-co-located BS or from BS and Remote Radio Heads, RRHs, or Remote Radio Units, RRUs). The well-known examples of combined CA and multi-point communication are Distributed Antenna Systems, or DAS, RRH, RRU, Coordinated Multi-Point, or CoMP, transmission/reception etc. The teachings herein are applicable to CCs in a CA context, and/or to CoMP.
Turning to positioning examples, there are a number of positioning methods known for determining the location of a target wireless device, which can be a UE, mobile relay, PDA, a Machine Type Communication, MTC, device (also known as “M2M” device), a laptop or other computer, a modem or other network adaptor, an eNB or other radio network node, a Location Measurement Unit, LMU, or other dedicated positioning node, or essentially any other type of wireless communication apparatus. In any case, the position of the target device is determined by using one or more positioning measurements, which can be performed by a suitable measuring node or the target device.
In LTE, an Evolved Serving Mobile Location Center or E-SMLC operates as positioning node, providing various positioning-related services and functions. For example, the positioning node configures the target device to perform one or more positioning measurements, depending upon the positioning method and/or requirements involved. The positioning measurements are used by the target device or by a measuring node or by the positioning node to determine the location of the target device. In LTE the positioning node communicates with UE using LTE positioning protocol, LPP, and with eNBs using LTE positioning protocol annex, or LPPa.
There are several well known positioning methods used in wireless communication networks, e.g., in LTE and other cellular networks. Examples include satellite methods, where positioning measurements are performed by the target device on signals received from navigational satellites and are used for determining the target device's location. For example either GNSS or A-GNSS (e.g. A-GPS, Galileo, COMPASS, GANSS, etc.) measurements are used for determining position of a UE or other target device.
The observed time difference of arrival or OTDOA method uses target device measurements related to time difference of arrival of signals from network radio nodes for determining the position of the target device. In an LTE example, reference signal received time difference, or RSTD, measurements are performed by a UE in a LTE network, for positioning the UE.
Similarly, with uplink time difference of arrival or UTDOA techniques, a measuring node performs measurements on uplink signals received from a target device. The measuring node may be a LMU in a LTE or other cellular network and the target device may be a UE. A positioning node or other location server in the network may use the LMU measurements from multiple LMUs for determining the position of the target device.
Another approach uses enhanced Cell ID or E-CID. Here, the cell ID of a serving and/or a neighboring cell and at least one additional radio measurement performed by the target device or by a radio node. For example, the E-CID method typically uses any combination of cell ID and radio measurements, such as UE Rx-Tx time difference, BS Rx-Tx time difference, timing advance, TA, measured by the BS, LTE RSRP and/or RSRQ, HSPA CPICH measurements, angle of arrival, AoA, measured by the BS on UE transmitted signals, etc., for determining the position of the target device.
Hybrid methods are also known. A hybrid positioning method incorporates positioning measurements related to more than one positioning method, for determining the position of the target device. For example, a hybrid method may use A-GNSS measurements and OTDOA RSTD measurements for determining the position of the target device. Hybrid methods can improve the overall accuracy of positioning, as compared to that obtained based on an individual method.
With the above information in mind, it will be appreciated that a UE or other wireless device or apparatus operating within a wireless communication network may have to make numerous types of radio signal or other measurements, e.g., on a repeating or triggered basis. For example, a UE may be required to perform certain radio measurement in the DL and/or UL subframes of one or more target cells, for use in various tasks.